1. Field of the Invention
This invention pertains generally to bolting assemblies particularly designed for use in strengthening mine roofs, and more particularly to anochor bolt assemblies of the type wherein a quick-setting adhesive is used to initially secure the bolt assembly in a predrilled bore hole.
2. Discussion of the Prior Art
Two different types of anchor bolts have been utilized for strengthening roofs in tunnels and coal mines. The older type is a mechanical anchor which expands within the bore hole to engage the sides of the bore hole upon threading a bolt into the expandable anchor member. In more recent years, the use of mechanical type anchor bolt has been supplemented with the use of anchor bolt assemblies which are secured in the bore hole by the use of a quick-setting adhesive in the case of poor mine roof conditions where conventional bolting is not working.
In the adhesive type bolting system, an elongated hole is bored into the rock structure and a thin-skinned resin capsule which contains unmixed quantities of quick-setting adhesive resin and catalyst hardener resin materials is then positioned in the back of the bore hole. The anchor bolt assembly, which generally consists of an elongated cylindrical anchor member and a bolt threadably received in one end of the anchor, is then inserted into the bore hole with the anchor member being inserted first. The entire bolting assembly is then rotated with a power tool such as an impact wrench so that the anchor member ruptures the thin-skinned capsule and the rotation of the anchor member subsequently mixes the adhesive resin and catalyst hardener resin and flows it uniformly about the bore hole and the outer surface of the anchor member. Rotation is ceased and the resin sets or hardens in a matter of seconds. After the resin has set, the bolt is again rotated such that it threadably advances into the anchor member which is now secured within the bore hole in order to draw the bolt head, or the bearing plate lying under the bolt head, up against the face of the rocklike structure about the opening of the bore hole.
The adhesive-type bolting assembly has the advantage that the adhesive strengthens the surrounding rock formation as well as anchors the bolt assembly and in addition, the bolts may be torqued up to tighten up again at some later time after the initial installation if required, which is not always possible with the mechanical type anchor, as it can tend to lose its grip to the side walls of the bore hole.
A good example of the resin-type anchor bolt assembly is illustrated in U.S. Pat. No. 3,877,235, issued Apr. 15, 1975. This anchor bolt assembly utilizes a stop means which is secured to the same end of the anchor member that threadably receives the bolt. The stop permits the entire bolt assembly to be rotated as a unit for mixing and spreading the resin adhesive. Once the resin adhesive is set, the bolt is again torqued, and since the anchor member is rigidly anchored within the bore hole, the stop means is sheared by the bolt so that the bolt may thereafter threadably advance into the anchor member and be drawn up tight against the outer face of the rocklike structure. The present invention relates to an improvement of this anchor bolt assembly.
U.S. Pat. No. 3,188,815 issued June 15, 1965, illustrates another resin-type bolt assembly. However, this anchor bolt assembly also illustrates a mechanical type anchor used in combination with the resin anchor. The present invention in one embodiment is also an improvment on this combination anchor bolt assembly, and it is also an object of the present invention to provide a less complex anchor bolt assembly structure which is more economical to manufactue.